Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.73   8.751%   $64.957   $64.96   $64.95   $65.00  
  Purchase #2 $44.44   5.452%   $46.8629   $46.86   $46.85   $46.90  
  Purchase #3 $120.74   4.580%   $126.2699   $126.27   $126.25   $126.30  
  Purchase #4 $196.50   5.181%   $206.6807   $206.68   $206.70   $206.70  
  Purchase #5 $227.44   6.730%   $242.7467   $242.75   $242.75   $242.70  
  Purchase #6 $84.52   8.846%   $91.9966   $92.00   $92.00   $92.00  
  Purchase #7 $30.68   13.487%   $34.8178   $34.82   $34.80   $34.80  
  7 purchase totals = $764.05       $814.3316   $814.34   $814.30   $814.40